1. Field of the Invention
The present invention relates to a tap hole drilling machine for producing a molten iron in a blast furnace molten iron making process. The present invention further relates to a drill bit for use in the tap hole drilling machine, and a tap hole drilling method. Particularly, the present invention relates to a tap hole drilling machine, a drill bit for use in it, and a tap hole drilling method, in which a high pressure nitrogen gas is used as a carrying gas for the tap hole drilling, and water mist mixed with cold water is spouted to cool the drill bit, so that the refractory material of the tap hole can be speedily drilled, thereby efficiently carrying out the tap hole drilling operation.
2. Description of the Prior Art
Generally in the blast furnace operation, as shown in FIG. 1, a plurality of tap holes 104 which are formed on the bottom of a blast furnace 100 are either periodically drilled by using a tap hole drilling machine 110, or the tap holes are drilled by using a round bar and by hitting by means of a hammer (not shown in the drawings). Then a slag 101 and a molten iron 120 are tapped through the tap hole 104.
The tap holes 104 are variously different depending on the blast furnace 100, but generally the depth from the blast furnace shell 100a to the inner region of the blast furnace is about 3 m.
Generally in a blast furnace 100 having an interior capacity of 3000 m.sup.3 or more, there are 3-4 tap holes 104 in a blast furnace 100. Among them, one is periodically repaired, while 2-3 of them are used in turns. Generally, the molten iron tapping time is 120-150 minutes.
Now the operation of the blast furnace will be described in detail. That is, the molten iron 120 and the slag 101 are tapped through the tap hole 104 which is formed in a tap hole wall 105 of FIG. 1. Upon completion of the tapping of the molten iron 120 and the slag 101, the tap hole 104 is closed by means of a refractory material 103. Under this condition, the refractory material 103 is calcined by the high pressure and the high temperature of the internal region of the blast furnace 100, and therefore, the strength of the refractory material is increased. When an operation through one tap hole 104 is completed, another tap hole is used, and in this manner, all the tap holes 104 are ultimately used.
Thus, upon completion of the operation through one tap hole 104, the relevant tap hole 104 is closed. As the time elapses, the refractory material 103 which has been closing the tap hole 104 is more calcined. Therefore, when the tap hole 104 is drilled for reuse, the drilling becomes very difficult.
Meanwhile in the conventional drilling operation, the tap hole 104 of the wall 105 is drilled by using a drill rod 106 and drill bit 107 which is fitted to a main body 118 of the tap hole drilling machine. Or the tap hole 104 is drilled by hammering and by using a round bar.
Under this condition, the refractory material 103 has been calcined and hardened within the blast furnace 100, and therefore, due to impacts of the drilling and the hammering, cracks are easily formed. Consequently, the refractory material 103 is detached in the blast furnace 100, and a gap is formed. Therefore the melt is leaked through the gap, and this leakage molten iron forms a solidified iron (to be called "inside crack") P, with the result that the drilling is rendered significantly more difficult. Accordingly, in the region of the solidified iron P, the drilling efficiency is significantly lowered.
Therefore, in the case where the drilling or hammering becomes difficult, a last means is applied in such a manner that oxygen is injected through a pipe (not shown in the drawings), and that the solidified iron P is dissolved, thereby opening the tap hole 104.
However, in the case where oxygen is injected, the flame of oxygen expands the tap hole 104 or damages the tap hole 104. Further, the opening time for the tan hole 104 is extended, and therefore, the molten iron tapping time is shortened, with the result that the production amount per day is decreased.
This oxygen opening operation usually consumes 20 minutes or more, and therefore, the production of the molten iron is delayed. Meanwhile to the workers, an unexpected tapping of the molten iron 120 and the slag 101 may cause an accident. Further, the management of the amount of the molten iron within the blast furnace 100 and the control of the blast furnace conditions become more difficult. Further, in order to control the blast furnace condition, a continuous molten iron tapping has to be carried out, and thus, the environment for the operation of the blast furnace becomes disadvantageous.
In this conventional tap hole drilling method, the drill rod 106 and the drill bit 107 are threadably fastened together, and this assembly is installed on the tap hole drilling machine 110. Further, in order to discharge the opening debris such as refractory material chips from the tap hole 104 during the tap hole drilling operation, a compressed air of 6 Kg/cm.sup.2 is injected from the main body 118 of the tap hole drilling machine 110 toward a flow path 106a of the drill rod 106. Thus the compressed air is spouted through a small blowing hole 124 of the drill bit 107 into the tap hole 104.
Further, the drill bit which is used in the conventional opening operation is provided with 4 blowing holes 124 which pass through a drill body 107a. The compressed air is injected from an air supply line 119 through the flow path 106a of the drill rod 106 and the main body 118 into the tap hole 104. The blowing holes 124 consist of one straight hole and three inclined holes having an angle of 30.degree.. A spouting mouth 71 is formed at the terminus of the straight blowing hole 124 in FIG. 1.
However, in the drill bit 107 which is used in the conventional tap hole opening method, there is almost no inclination (tapering) on the outer circumference of the drill body 107a. Further, grooves 107c which are formed between bit blades 107b on the drill body 107a are narrow. Therefore, the opening debris such as the refractory material chins cannot be efficiently discharged. Further the compressed air for cooling by passing through the small blowing holes 124 shows a lowered spouting pressure due to the pressure loss. Further, due to the use of the compressed air for cooling, the drill bit 107 is easily deteriorated in the environment of a high temperature of 1300.degree. C., thereby aggravating the drilling performance.
Further, the spouting pressure of the compressed air is lowered during the drilling operation, and the flow path for the compressed air is clogged by the opening debris, with the result that the drill bit 107 is distorted within the tap hole 104. When the distortion occurs, the discharge of the opening debris is further made difficult. Then the drill bit 107 is more heated within the tap hole 104, and therefore, the drill bit 107 is further deteriorated. This vicious cycle is repeated.
Further, the drill bit 107 is threadably and detachably coupled to the drill rod 106, and the drill rod 106 has to withstand against impacts and the revolution load during the drilling. Further, the drill rod 106 is made of an expensive high strength steel, and therefore, it has to be used with an utmost care, this being a troublesome task.
FIG. 2 illustrates the process steps for opening the tap hole 104 by using the conventional tap hole drilling machine and the conventional drill bit 107.
In this conventional process of FIG. 2, first a step 152 is carried out in which the molten iron 120 and the slag 101 are tapped from the blast furnace 100, then the tap hole is closed by using a refractory material 103, and then, the refractory material 103 is drilled by about 2 m by using the drill bit 107 before the refractory material undergoes a complete calcination.
Then a step 154 is carried out in which the drill rod 106 and the drill bit 107 are removed from the tap hole drilling machine 110.
Then a step 156 is carried out in which a round bar 122 is installed on the tap hole drilling machine to pierce the remaining portion of the refractory material 103.
Then a step 158 is carried out in which, if the piercing by means of the round bar 122 has failed at the step 156, a repiercing is carried out by injecting oxygen.
Then a step 160 is carried out in which it waits until the next molten iron tapping, in a state with the tap hole 104 pierced by the round-bar 122.
Then a step 162 is carried out in which if the molten iron tapping is to be started, the round bar 122 is withdrawn out of the tap hole 104 by using the tap hole drilling machine 110.
Then a step 164 is carried out in which a molten iron tapping operation is carried out through the open tap hole 104.
In this conventional tap hole drilling method, the drill bit and the drill rod have to be replaced with a round bar, and it has to wait in a state with the round bar inserted into the tap hole. Therefore, the tap hole drilling operation is complicated, and much time is consumed, with the result that an efficient tap hole drilling becomes impossible.